OK, let's crack this. We're given 852 and our task is to multiply it by 407. Essentially, we'll be adding 852 to itself 407 times.
Step 1: 0 + 852 = 852
Step 2: 852 + 852 = 1704
Step 3: 1704 + 852 = 2556
Step 4: 2556 + 852 = 3408
Step 5: 3408 + 852 = 4260
Step 6: 4260 + 852 = 5112
Step 7: 5112 + 852 = 5964
Step 8: 5964 + 852 = 6816
Step 9: 6816 + 852 = 7668
Step 10: 7668 + 852 = 8520
Step 11: 8520 + 852 = 9372
Step 12: 9372 + 852 = 10224
Step 13: 10224 + 852 = 11076
Step 14: 11076 + 852 = 11928
Step 15: 11928 + 852 = 12780
Step 16: 12780 + 852 = 13632
Step 17: 13632 + 852 = 14484
Step 18: 14484 + 852 = 15336
Step 19: 15336 + 852 = 16188
Step 20: 16188 + 852 = 17040
Step 21: 17040 + 852 = 17892
Step 22: 17892 + 852 = 18744
Step 23: 18744 + 852 = 19596
Step 24: 19596 + 852 = 20448
Step 25: 20448 + 852 = 21300
Step 26: 21300 + 852 = 22152
Step 27: 22152 + 852 = 23004
Step 28: 23004 + 852 = 23856
Step 29: 23856 + 852 = 24708
Step 30: 24708 + 852 = 25560
Step 31: 25560 + 852 = 26412
Step 32: 26412 + 852 = 27264
Step 33: 27264 + 852 = 28116
Step 34: 28116 + 852 = 28968
Step 35: 28968 + 852 = 29820
Step 36: 29820 + 852 = 30672
Step 37: 30672 + 852 = 31524
Step 38: 31524 + 852 = 32376
Step 39: 32376 + 852 = 33228
Step 40: 33228 + 852 = 34080
Step 41: 34080 + 852 = 34932
Step 42: 34932 + 852 = 35784
Step 43: 35784 + 852 = 36636
Step 44: 36636 + 852 = 37488
Step 45: 37488 + 852 = 38340
Step 46: 38340 + 852 = 39192
Step 47: 39192 + 852 = 40044
Step 48: 40044 + 852 = 40896
Step 49: 40896 + 852 = 41748
Step 50: 41748 + 852 = 42600
Step 51: 42600 + 852 = 43452
Step 52: 43452 + 852 = 44304
Step 53: 44304 + 852 = 45156
Step 54: 45156 + 852 = 46008
Step 55: 46008 + 852 = 46860
Step 56: 46860 + 852 = 47712
Step 57: 47712 + 852 = 48564
Step 58: 48564 + 852 = 49416
Step 59: 49416 + 852 = 50268
Step 60: 50268 + 852 = 51120
Step 61: 51120 + 852 = 51972
Step 62: 51972 + 852 = 52824
Step 63: 52824 + 852 = 53676
Step 64: 53676 + 852 = 54528
Step 65: 54528 + 852 = 55380
Step 66: 55380 + 852 = 56232
Step 67: 56232 + 852 = 57084
Step 68: 57084 + 852 = 57936
Step 69: 57936 + 852 = 58788
Step 70: 58788 + 852 = 59640
Step 71: 59640 + 852 = 60492
Step 72: 60492 + 852 = 61344
Step 73: 61344 + 852 = 62196
Step 74: 62196 + 852 = 63048
Step 75: 63048 + 852 = 63900
Step 76: 63900 + 852 = 64752
Step 77: 64752 + 852 = 65604
Step 78: 65604 + 852 = 66456
Step 79: 66456 + 852 = 67308
Step 80: 67308 + 852 = 68160
Step 81: 68160 + 852 = 69012
Step 82: 69012 + 852 = 69864
Step 83: 69864 + 852 = 70716
Step 84: 70716 + 852 = 71568
Step 85: 71568 + 852 = 72420
Step 86: 72420 + 852 = 73272
Step 87: 73272 + 852 = 74124
Step 88: 74124 + 852 = 74976
Step 89: 74976 + 852 = 75828
Step 90: 75828 + 852 = 76680
Step 91: 76680 + 852 = 77532
Step 92: 77532 + 852 = 78384
Step 93: 78384 + 852 = 79236
Step 94: 79236 + 852 = 80088
Step 95: 80088 + 852 = 80940
Step 96: 80940 + 852 = 81792
Step 97: 81792 + 852 = 82644
Step 98: 82644 + 852 = 83496
Step 99: 83496 + 852 = 84348
Step 100: 84348 + 852 = 85200
Step 101: 85200 + 852 = 86052
Step 102: 86052 + 852 = 86904
Step 103: 86904 + 852 = 87756
Step 104: 87756 + 852 = 88608
Step 105: 88608 + 852 = 89460
Step 106: 89460 + 852 = 90312
Step 107: 90312 + 852 = 91164
Step 108: 91164 + 852 = 92016
Step 109: 92016 + 852 = 92868
Step 110: 92868 + 852 = 93720
Step 111: 93720 + 852 = 94572
Step 112: 94572 + 852 = 95424
Step 113: 95424 + 852 = 96276
Step 114: 96276 + 852 = 97128
Step 115: 97128 + 852 = 97980
Step 116: 97980 + 852 = 98832
Step 117: 98832 + 852 = 99684
Step 118: 99684 + 852 = 100536
Step 119: 100536 + 852 = 101388
Step 120: 101388 + 852 = 102240
Step 121: 102240 + 852 = 103092
Step 122: 103092 + 852 = 103944
Step 123: 103944 + 852 = 104796
Step 124: 104796 + 852 = 105648
Step 125: 105648 + 852 = 106500
Step 126: 106500 + 852 = 107352
Step 127: 107352 + 852 = 108204
Step 128: 108204 + 852 = 109056
Step 129: 109056 + 852 = 109908
Step 130: 109908 + 852 = 110760
Step 131: 110760 + 852 = 111612
Step 132: 111612 + 852 = 112464
Step 133: 112464 + 852 = 113316
Step 134: 113316 + 852 = 114168
Step 135: 114168 + 852 = 115020
Step 136: 115020 + 852 = 115872
Step 137: 115872 + 852 = 116724
Step 138: 116724 + 852 = 117576
Step 139: 117576 + 852 = 118428
Step 140: 118428 + 852 = 119280
Step 141: 119280 + 852 = 120132
Step 142: 120132 + 852 = 120984
Step 143: 120984 + 852 = 121836
Step 144: 121836 + 852 = 122688
Step 145: 122688 + 852 = 123540
Step 146: 123540 + 852 = 124392
Step 147: 124392 + 852 = 125244
Step 148: 125244 + 852 = 126096
Step 149: 126096 + 852 = 126948
Step 150: 126948 + 852 = 127800
Step 151: 127800 + 852 = 128652
Step 152: 128652 + 852 = 129504
Step 153: 129504 + 852 = 130356
Step 154: 130356 + 852 = 131208
Step 155: 131208 + 852 = 132060
Step 156: 132060 + 852 = 132912
Step 157: 132912 + 852 = 133764
Step 158: 133764 + 852 = 134616
Step 159: 134616 + 852 = 135468
Step 160: 135468 + 852 = 136320
Step 161: 136320 + 852 = 137172
Step 162: 137172 + 852 = 138024
Step 163: 138024 + 852 = 138876
Step 164: 138876 + 852 = 139728
Step 165: 139728 + 852 = 140580
Step 166: 140580 + 852 = 141432
Step 167: 141432 + 852 = 142284
Step 168: 142284 + 852 = 143136
Step 169: 143136 + 852 = 143988
Step 170: 143988 + 852 = 144840
Step 171: 144840 + 852 = 145692
Step 172: 145692 + 852 = 146544
Step 173: 146544 + 852 = 147396
Step 174: 147396 + 852 = 148248
Step 175: 148248 + 852 = 149100
Step 176: 149100 + 852 = 149952
Step 177: 149952 + 852 = 150804
Step 178: 150804 + 852 = 151656
Step 179: 151656 + 852 = 152508
Step 180: 152508 + 852 = 153360
Step 181: 153360 + 852 = 154212
Step 182: 154212 + 852 = 155064
Step 183: 155064 + 852 = 155916
Step 184: 155916 + 852 = 156768
Step 185: 156768 + 852 = 157620
Step 186: 157620 + 852 = 158472
Step 187: 158472 + 852 = 159324
Step 188: 159324 + 852 = 160176
Step 189: 160176 + 852 = 161028
Step 190: 161028 + 852 = 161880
Step 191: 161880 + 852 = 162732
Step 192: 162732 + 852 = 163584
Step 193: 163584 + 852 = 164436
Step 194: 164436 + 852 = 165288
Step 195: 165288 + 852 = 166140
Step 196: 166140 + 852 = 166992
Step 197: 166992 + 852 = 167844
Step 198: 167844 + 852 = 168696
Step 199: 168696 + 852 = 169548
Step 200: 169548 + 852 = 170400
Step 201: 170400 + 852 = 171252
Step 202: 171252 + 852 = 172104
Step 203: 172104 + 852 = 172956
Step 204: 172956 + 852 = 173808
Step 205: 173808 + 852 = 174660
Step 206: 174660 + 852 = 175512
Step 207: 175512 + 852 = 176364
Step 208: 176364 + 852 = 177216
Step 209: 177216 + 852 = 178068
Step 210: 178068 + 852 = 178920
Step 211: 178920 + 852 = 179772
Step 212: 179772 + 852 = 180624
Step 213: 180624 + 852 = 181476
Step 214: 181476 + 852 = 182328
Step 215: 182328 + 852 = 183180
Step 216: 183180 + 852 = 184032
Step 217: 184032 + 852 = 184884
Step 218: 184884 + 852 = 185736
Step 219: 185736 + 852 = 186588
Step 220: 186588 + 852 = 187440
Step 221: 187440 + 852 = 188292
Step 222: 188292 + 852 = 189144
Step 223: 189144 + 852 = 189996
Step 224: 189996 + 852 = 190848
Step 225: 190848 + 852 = 191700
Step 226: 191700 + 852 = 192552
Step 227: 192552 + 852 = 193404
Step 228: 193404 + 852 = 194256
Step 229: 194256 + 852 = 195108
Step 230: 195108 + 852 = 195960
Step 231: 195960 + 852 = 196812
Step 232: 196812 + 852 = 197664
Step 233: 197664 + 852 = 198516
Step 234: 198516 + 852 = 199368
Step 235: 199368 + 852 = 200220
Step 236: 200220 + 852 = 201072
Step 237: 201072 + 852 = 201924
Step 238: 201924 + 852 = 202776
Step 239: 202776 + 852 = 203628
Step 240: 203628 + 852 = 204480
Step 241: 204480 + 852 = 205332
Step 242: 205332 + 852 = 206184
Step 243: 206184 + 852 = 207036
Step 244: 207036 + 852 = 207888
Step 245: 207888 + 852 = 208740
Step 246: 208740 + 852 = 209592
Step 247: 209592 + 852 = 210444
Step 248: 210444 + 852 = 211296
Step 249: 211296 + 852 = 212148
Step 250: 212148 + 852 = 213000
Step 251: 213000 + 852 = 213852
Step 252: 213852 + 852 = 214704
Step 253: 214704 + 852 = 215556
Step 254: 215556 + 852 = 216408
Step 255: 216408 + 852 = 217260
Step 256: 217260 + 852 = 218112
Step 257: 218112 + 852 = 218964
Step 258: 218964 + 852 = 219816
Step 259: 219816 + 852 = 220668
Step 260: 220668 + 852 = 221520
Step 261: 221520 + 852 = 222372
Step 262: 222372 + 852 = 223224
Step 263: 223224 + 852 = 224076
Step 264: 224076 + 852 = 224928
Step 265: 224928 + 852 = 225780
Step 266: 225780 + 852 = 226632
Step 267: 226632 + 852 = 227484
Step 268: 227484 + 852 = 228336
Step 269: 228336 + 852 = 229188
Step 270: 229188 + 852 = 230040
Step 271: 230040 + 852 = 230892
Step 272: 230892 + 852 = 231744
Step 273: 231744 + 852 = 232596
Step 274: 232596 + 852 = 233448
Step 275: 233448 + 852 = 234300
Step 276: 234300 + 852 = 235152
Step 277: 235152 + 852 = 236004
Step 278: 236004 + 852 = 236856
Step 279: 236856 + 852 = 237708
Step 280: 237708 + 852 = 238560
Step 281: 238560 + 852 = 239412
Step 282: 239412 + 852 = 240264
Step 283: 240264 + 852 = 241116
Step 284: 241116 + 852 = 241968
Step 285: 241968 + 852 = 242820
Step 286: 242820 + 852 = 243672
Step 287: 243672 + 852 = 244524
Step 288: 244524 + 852 = 245376
Step 289: 245376 + 852 = 246228
Step 290: 246228 + 852 = 247080
Step 291: 247080 + 852 = 247932
Step 292: 247932 + 852 = 248784
Step 293: 248784 + 852 = 249636
Step 294: 249636 + 852 = 250488
Step 295: 250488 + 852 = 251340
Step 296: 251340 + 852 = 252192
Step 297: 252192 + 852 = 253044
Step 298: 253044 + 852 = 253896
Step 299: 253896 + 852 = 254748
Step 300: 254748 + 852 = 255600
Step 301: 255600 + 852 = 256452
Step 302: 256452 + 852 = 257304
Step 303: 257304 + 852 = 258156
Step 304: 258156 + 852 = 259008
Step 305: 259008 + 852 = 259860
Step 306: 259860 + 852 = 260712
Step 307: 260712 + 852 = 261564
Step 308: 261564 + 852 = 262416
Step 309: 262416 + 852 = 263268
Step 310: 263268 + 852 = 264120
Step 311: 264120 + 852 = 264972
Step 312: 264972 + 852 = 265824
Step 313: 265824 + 852 = 266676
Step 314: 266676 + 852 = 267528
Step 315: 267528 + 852 = 268380
Step 316: 268380 + 852 = 269232
Step 317: 269232 + 852 = 270084
Step 318: 270084 + 852 = 270936
Step 319: 270936 + 852 = 271788
Step 320: 271788 + 852 = 272640
Step 321: 272640 + 852 = 273492
Step 322: 273492 + 852 = 274344
Step 323: 274344 + 852 = 275196
Step 324: 275196 + 852 = 276048
Step 325: 276048 + 852 = 276900
Step 326: 276900 + 852 = 277752
Step 327: 277752 + 852 = 278604
Step 328: 278604 + 852 = 279456
Step 329: 279456 + 852 = 280308
Step 330: 280308 + 852 = 281160
Step 331: 281160 + 852 = 282012
Step 332: 282012 + 852 = 282864
Step 333: 282864 + 852 = 283716
Step 334: 283716 + 852 = 284568
Step 335: 284568 + 852 = 285420
Step 336: 285420 + 852 = 286272
Step 337: 286272 + 852 = 287124
Step 338: 287124 + 852 = 287976
Step 339: 287976 + 852 = 288828
Step 340: 288828 + 852 = 289680
Step 341: 289680 + 852 = 290532
Step 342: 290532 + 852 = 291384
Step 343: 291384 + 852 = 292236
Step 344: 292236 + 852 = 293088
Step 345: 293088 + 852 = 293940
Step 346: 293940 + 852 = 294792
Step 347: 294792 + 852 = 295644
Step 348: 295644 + 852 = 296496
Step 349: 296496 + 852 = 297348
Step 350: 297348 + 852 = 298200
Step 351: 298200 + 852 = 299052
Step 352: 299052 + 852 = 299904
Step 353: 299904 + 852 = 300756
Step 354: 300756 + 852 = 301608
Step 355: 301608 + 852 = 302460
Step 356: 302460 + 852 = 303312
Step 357: 303312 + 852 = 304164
Step 358: 304164 + 852 = 305016
Step 359: 305016 + 852 = 305868
Step 360: 305868 + 852 = 306720
Step 361: 306720 + 852 = 307572
Step 362: 307572 + 852 = 308424
Step 363: 308424 + 852 = 309276
Step 364: 309276 + 852 = 310128
Step 365: 310128 + 852 = 310980
Step 366: 310980 + 852 = 311832
Step 367: 311832 + 852 = 312684
Step 368: 312684 + 852 = 313536
Step 369: 313536 + 852 = 314388
Step 370: 314388 + 852 = 315240
Step 371: 315240 + 852 = 316092
Step 372: 316092 + 852 = 316944
Step 373: 316944 + 852 = 317796
Step 374: 317796 + 852 = 318648
Step 375: 318648 + 852 = 319500
Step 376: 319500 + 852 = 320352
Step 377: 320352 + 852 = 321204
Step 378: 321204 + 852 = 322056
Step 379: 322056 + 852 = 322908
Step 380: 322908 + 852 = 323760
Step 381: 323760 + 852 = 324612
Step 382: 324612 + 852 = 325464
Step 383: 325464 + 852 = 326316
Step 384: 326316 + 852 = 327168
Step 385: 327168 + 852 = 328020
Step 386: 328020 + 852 = 328872
Step 387: 328872 + 852 = 329724
Step 388: 329724 + 852 = 330576
Step 389: 330576 + 852 = 331428
Step 390: 331428 + 852 = 332280
Step 391: 332280 + 852 = 333132
Step 392: 333132 + 852 = 333984
Step 393: 333984 + 852 = 334836
Step 394: 334836 + 852 = 335688
Step 395: 335688 + 852 = 336540
Step 396: 336540 + 852 = 337392
Step 397: 337392 + 852 = 338244
Step 398: 338244 + 852 = 339096
Step 399: 339096 + 852 = 339948
Step 400: 339948 + 852 = 340800
Step 401: 340800 + 852 = 341652
Step 402: 341652 + 852 = 342504
Step 403: 342504 + 852 = 343356
Step 404: 343356 + 852 = 344208
Step 405: 344208 + 852 = 345060
Step 406: 345060 + 852 = 345912
Step 407: 345912 + 852 = 346764

So, 852*407 = 346764